Cell lines established from Balb-derived xenotropic murine leukemia virus pseudotype of the m1 isolate of Moloney murine sarcoma virus (m1MSV BMuX)-induced tumors in Japanese quail showed genetically stable alterations in MSV-specific polyprotein metabolism. Sera from tumored quail and regressor quail contained high titers of type-specific antibodies to BMuX envelope gene determinants, variable titers of antibodies to MSV or BMuX group antigen gene determinants and no detectable antibody to the putative transforming protein of MSV. Permuted envelope gene products of recombinant murine leukemia viruses (MuLV's) were examined by two-dimensional peptide maps. Analogous envelope glycoproteins were found in several virus-free mouse lymphoma cells.